Aquarium Volume Calculator
Aquarium Volume Calculator
Find how many gallons or liters a fish tank holds from its size, for rectangular, cylinder, bowfront, hexagon and corner tanks, with the real amount of water once the glass, the gap below the rim and the gravel are taken out, and what the tank weighs when full.
Footprint
Side section
Against standard tanks
Volume = footprint area times height; 231 cubic inches make one US gallon and 1,000 cubic centimeters make one liter. Measure the outside of the tank; the water volume takes off the glass on the sides and bottom, the gap left below the rim and the gravel or sand layer, and a little extra water sits between the grains. Weights use 8.34 lb per US gallon for fresh water, 2.5 percent more for seawater, 1.5 kg per liter for gravel or sand and 2.5 kg per liter for glass, so treat them as estimates. Heater and filter sizes are common rules of thumb, not fixed rules. The CSV, image and printed report contain the values you entered, nothing preloaded.
How to use this tool
Pick the tank shape and units, then measure the outside of the tank: length, width front to back and height for a standard rectangular tank. The volume to the brim appears at the top in gallons and liters, with the real amount of water and the weight when full.
The glass thickness, the gap you leave below the rim and the depth of gravel or sand start at typical values; change them to match your tank. Switch to centimeters and the numbers already entered are converted. The drawings show the footprint and a section through the tank, and the chart puts it beside common standard sizes.
How aquarium volume is worked out
Every shape here has straight sides, so the volume is the area of the footprint times the height. A rectangle is length times width, a cylinder is 3.1416 times the diameter squared divided by 4, a regular hexagon is 2.598 times the side squared, and a quarter circle corner tank is a quarter of a circle with the side as its radius. A bowfront adds a segment of a circle to a rectangle, worked out from the length and the depth of the bow.
In inches, divide the cubic inches by 231 to get US gallons; in centimeters, divide the cubic centimeters by 1,000 to get liters. One US gallon is 3.785 liters and a UK gallon 4.546, so a tank sold in the UK as 20 gallons is about 24 US gallons.
How much water standard tanks really hold
| Tank | Size, in | To the brim | Actual water | Filled weight |
|---|---|---|---|---|
| 5.5 gallon | 16 x 8 x 10 | 5.5 gal | 3.5 gal | 50 lb |
| 10 gallon | 20 x 10 x 12 | 10.4 gal | 7.2 gal | 100 lb |
| 15 gallon | 24 x 12 x 12 | 15.0 gal | 10.5 gal | 140 lb |
| 20 gallon high | 24 x 12 x 16 | 19.9 gal | 15.2 gal | 180 lb |
| 20 gallon long | 30 x 12 x 12 | 18.7 gal | 13.1 gal | 170 lb |
| 29 gallon | 30 x 12 x 18 | 28.1 gal | 22.1 gal | 250 lb |
| 40 gallon breeder | 36 x 18 x 16 | 44.9 gal | 34.8 gal | 400 lb |
| 40 gallon long | 48 x 12 x 16 | 39.9 gal | 30.7 gal | 360 lb |
| 55 gallon | 48 x 13 x 21 | 56.7 gal | 46.3 gal | 510 lb |
| 75 gallon | 48 x 18 x 21 | 78.5 gal | 64.7 gal | 690 lb |
| 90 gallon | 48 x 18 x 24 | 89.8 gal | 75.6 gal | 790 lb |
| 120 gallon | 48 x 24 x 24 | 119.7 gal | 101.3 gal | 1,050 lb |
| 125 gallon | 72 x 18 x 21 | 117.8 gal | 97.3 gal | 1,040 lb |
| 150 gallon | 72 x 18 x 28 | 157.1 gal | 135.5 gal | 1,380 lb |
| 180 gallon | 72 x 24 x 24 | 179.5 gal | 152.4 gal | 1,560 lb |
Nominal sizes; actual water allows for 0.19 inch glass, 2 inches of gravel and a water line 1 inch below the rim. Filled weights are freshwater estimates.
A worked example you can check on paper
A standard 55 gallon tank measures 48 x 13 x 21 inches. That is 13,104 cubic inches, and 13,104 divided by 231 is 56.7 gallons to the brim.
Inside 0.19 inch glass the floor is 47.62 by 12.62 inches, or 601 square inches. Take the bottom glass, 2 inches of gravel and a 1 inch gap off the 21 inch height and the water is 17.81 inches deep: 601 times 17.81 is 10,703 cubic inches, or 46.3 gallons. At 8.34 lb a gallon that water weighs about 387 lb; add about 65 lb of gravel and 55 lb of glass and the tank weighs roughly 506 lb full.
Mistakes that catch people out
Dosing by the label. Medicines and water conditioners are dosed by the water in the tank, not the size on the box. A 55 gallon tank with gravel and rock may hold 45 gallons or less.
Mixing US and UK gallons. A UK gallon is about 20 percent bigger, so the same tank is fewer UK gallons than US gallons.
Measuring the bow wrong. The bow is the extra depth in the middle, not the whole depth at the center.
Forgetting the stand. Water weighs 8.34 lb a gallon, and a filled tank is heavier than most furniture. Use a stand rated for the tank.
Popular calculations
Each opens the calculator with its own address, and every value can be changed once it is open.
Standard rectangular tanks
Metric tanks
Cylinder tanks
Bowfront tanks
Hexagon tanks
Corner tanks
Saltwater weight
How this was checked
The engine was tested in Node against hand calculations for every shape: rectangles and cylinders by formula, the bowfront segment and the corner tank inside the glass by numerical integration, and the hexagon inset against the reduced side length. Standard sizes match the familiar figures, such as 10.4 gallons for a 20 x 10 x 12 inch tank.
Every address in the lists above was then opened and checked for a distinct title, the right answer, drawings and charts that render, and clean CSV, image and print output containing only that calculation, at desktop, tablet and phone widths.
Common questions
How do I work out how many gallons my fish tank holds?
Measure the length, width and height in inches, multiply them together and divide by 231, the number of cubic inches in a US gallon. A 20 x 10 x 12 inch tank is 2,400 cubic inches, or 10.4 gallons.
How many liters does my aquarium hold?
Measure in centimeters, multiply length, width and height, and divide by 1,000. A 60 x 30 x 36 cm tank holds 64,800 cubic centimeters, which is 64.8 liters.
How much water does a 10 gallon tank really hold?
About 7.2 gallons once you allow for thin glass, 2 inches of gravel and a water line an inch below the rim. The 10 gallon figure is the size of the box, and most tanks hold 25 to 35 percent less water than their label.
How much does a 55 gallon aquarium weigh when full?
About 510 lb with 2 inches of gravel, going by the calculator’s estimate, and more with rock or a thick glass bottom. Many keepers use 10 lb for every gallon of tank size, about 550 lb, as a safe round figure when choosing a stand.
How do I measure a bowfront tank?
Measure the length straight across the front, the depth from back to front at one end, and the depth in the middle. The bow is the middle depth minus the end depth; enter the end depth and the bow, and the calculator adds the curved part as a segment of a circle.
What size heater and filter does my tank need?
Common rules of thumb are 3 to 5 watts of heater for each gallon of water and a filter that moves 4 to 6 times the tank volume every hour. For a 20 gallon long that is about 40 to 65 W and 75 to 110 gallons per hour; a cold room or a heavily stocked tank needs the top of the range.
Related Calculators and Reference
- Pool Volume Calculator: gallons and liters in a pool or hot tub.
- Volume Converter: liters, US gallons, UK gallons and more.
- Gravel Calculator: tons and bags of gravel for an area.
- Water Tank Sizing Calculator: storage tank size for a supply.
- Tank Volume Calculator: volume at any water level for horizontal, vertical and rectangular tanks.
- NIST: Unit Conversion: the gallon and liter definitions used here.